Struff mixed power, including 22 aces, with panache in a promising display ahead of the Australian Open, where he has drawn Australian Matthew Ebden in the opening round.

It was the sort of workout Carreno Busta would have appreciated after previously spending no more than 10 minutes on court this week because of retirements.

The Spanish world No.23 reached the fourth round in Melbourne last year before losing to eventual finalist Marin Cilic.

World No.13 Fognini was the other major quarter-final casualty, the second seed swept aside 6-3 6-1 by 2008 champion Philipp Kohlschreiber of Germany.

It was a listless display from Italian second seed Fognini, who called for the trainer at one stage and made little effort to chase down balls as the match wore on.

It came as a surprise to veteran Kohlschreiber, who is playing in Auckland for the 12th time.

"I don't know what happened to Fabio, he dropped a little bit, maybe he was injured, I'm not quite sure," he said.

"It's never easy to see someone on the other side when you don't know whether he's able to run at full power. But still, Fabio is Fabio, he doesn't need to move so much, but I am very happy with the way it went."

Seeds have been an endangered species this week. Top-seeded American John Isner was ousted in the second round, along with four-time champion David Ferrer, while Gael Monfils, Tomas Berdych and Roberto Bautista Agut were withdrawals.

Kohlschreiber's semi-final opponent on Friday will be the unseeded Tennys Sandgren. The American outclassed Argentina's Leonardo Mayer 6-3 7-6 (7-5).

New Zealand-raised British No.2 Cameron Norrie will face Struff after seeing off American Taylor Townsend 7-6 (7-3) 6-3.